(a) Field of the Invention
The present invention relates to a liquid crystal display, and an apparatus and method for driving the liquid crystal display.
(b) Description of the Related Art
Liquid crystal displays (LCDs) include two panels having pixel electrodes and a common electrode and a liquid crystal (LC) layer with dielectric anisotropy, which is interposed between the two panels. The liquid crystal layer is applied with electric field by applying voltages to the two electrodes, and the transmittance of light passing through the liquid crystal layer is adjusted by controlling the electric field, thereby obtaining desired images. The pixel electrodes are arranged in a matrix and connected to switching elements such as thin film transistors (TFTs). The switching elements selectively transmit data voltages from data lines in response to gate signals from gate lines. The common electrode covers entire surface of one of the two panels and is supplied with a common voltage.
In order to prevent image deterioration due to long-time application of the unidirectional electric field, polarity of data voltages with respect to the common voltage is reversed every frame, every row, or every dot. Along with the polarity inversion of the data voltages, a common voltage modulation is used to reduce power consumption. The common voltage modulation is to change the magnitude of the common voltage in synchronization with the polarity inversion of the data voltages instead of fixing the magnitude of the common voltage, thereby reducing the amplitude of the data voltages.
However, as described above, since the common electrode covers entire surface of one of the two panels, the magnitude of the common voltage applied to adjacent pixels may not be different. Therefore, the magnitude of the common voltage applied to the pixels in one row supplied with the data voltages at the same time should be equal, and thus the common voltage modulation may be not used for a dot inversion LCD.
In a line inversion LCD, different pixel rows are supplied with the data voltages at different times and the magnitude of the common voltage may be changed every row using the common voltage modulation. In this case, image data for a row from a signal controller are sequentially stored into a data driver together with an inversion signal for determining the polarity of the image data, and they are applied to the LCD panel assembly when all the image data for the row are stored into the data driver after one horizontal period from the start of the data storing. However, because the common voltage is directly applied to the LCD panel assembly not through the data driver, the inversion signal is delayed by a horizontal period than the periodic common voltage.
In the meantime, the line inversion often enhances flicker phenomenon. In an LCD for a cellular phone, etc., having a small display screen and a low operating frequency, image deterioration such as the flicker phenomenon is not a significant problem since the user hardly perceives the flicker. However, it becomes increasingly important as the size of the display screen of an LCD becomes large.